Catalyst stability as a factor in iridium‐mediated ortho‐deuteration

Crossover experiments show that iridium complexes such as Ir(cod)(Py)(PCy₃).PF₆ ( 1 ) and Ir(cod)(PPh₃)₂.BF₄ are inactivated after a comparatively short period during deuterium exchange reactions. This effect can be limited to some extent by optimizing the concentration at which exchange is performed, but altering physical parameters and adding labile ligands in an effort to stabilize reactive intermediates does not improve matters. Complexes of bidentate arsines and PN ligands and, in some cases, bidentate phosphines, exhibit better stability. Unexpectedly, following hydrogenolysis, 1 is able to mediate deuterium exchange from deuterium oxide into amides and N‐heterocycles at room temperature. Copyright © 2007 John Wiley & Sons, Ltd.